1. Field of the Invention
The present invention relates generally to the field of computer graphics systems, and more particularly to a system and method for storing and accessing data representative of an object in various levels of detail (LODs).
2. Related Art
Graphics systems are often used to display images of objects. A graphics system may store data representative of an object and display an image of the object using the stored data. Such a system may store several representations of an object, with each representation having a different level of detail (LOD). Data representations which have more detail are generally termed as finer level LODs and data representations which have a lesser amount of detail are termed as coarser level LODs.
The amount of detail stored in different LOD representations may be appreciated by drawing an analogy to the detail perceived by an observer while observing an object. For example, very little detail may be perceived by an observer while watching an automobile from a distance. On the other hand, several details such as doors, windows, mirrors will be perceived if the observer is sufficiently close to the automobile. A finer level LOD may include such additional details also.
Graphics systems often store the data corresponding to several LOD representations of an object in a secondary memory (e.g., a hard-drive used in workstations). The LOD data is then retrieved from the secondary memory into a main memory (e.g., random access memory) and processed to generate display signals corresponding to the object. The data is stored in a secondary memory generally due to the large amount of data in each LOD representation, and is retrieved into a main memory due to the faster access usually provided by the main memory. Thus, a graphics system may store a large amount of data corresponding to LOD representations, and at the same time have speedy access to the data by retrieving them into main memory.
Speedy access of the LOD data is often critical for acceptable performance of graphics systems. For example, an interactive application may need access to data corresponding to different portions of an object at different LODs within a short span of time. To generate display signals at an acceptable rate, a graphics system may need fast access to the required data.
However, the graphics system may not have such speedy access to the data, for example, as the data may not be present in the main memory. In such a situation, the required data may first need to be retrieved from the secondary memory into a memory, and then accessed by the graphics system. Due to the relatively slower accessing speed of the secondary memory and due to the multiple retrievals involved, the data may not be provided at a desired rate to the graphics systems. Accordingly, the graphics system may not be able to generate display signals at an acceptable rate. As a result, the display quality may be unacceptable in certain situations.